1. Field of the Invention
This invention relates to a truss type actuator having a plurality of (for example, two) displacing devices such as piezoelectric devices crossing at right angle, and respectively driven by alternating driving .voltages having a phase difference between them for generating a driving force owing to an elliptical movement of a chip member provided at crossing point of the displacing devices.
2. Description of the Related Art
Conventionally, a truss type piezoelectric actuator is known from Publication Gazette of Unexamined Japanese Patent Application Hei 8-289573 (hereinafter abbreviated as first prior art) or U.S. Pat. No. 4613782 (hereinafter abbreviated as second prior art).
In the first prior art, contacting faces at base ends of two piezoelectric devices (first piezoelectric device and second piezoelectric device) are fixed on a base member, and contacting faces at top ends of the piezoelectric devices are also fixed to a chip member provided at a cross point of the piezoelectric devices. The first prior art, however, does not teach the method for fixing the piezoelectric devices and the base member, and so on. On the other hand, in the second prior art, each piezoelectric device and a driving element are fixed by a resultant motion mechanism having a rigidity in a direction parallel to a displacing direction of the piezoelectric device and a flexibility in a direction perpendicular to the displacing direction of the piezoelectric device.
In the first prior art, when the first piezoelectric device is driven for displacing, a bending force acts on the second piezoelectric device in a transverse direction thereof, and the first piezoelectric device receives a reaction force from the second piezoelectric device. In case of fixing the base member and the chip member on each piezoelectric device by a material having a high rigidity, the displacement of the first piezoelectric device is restricted by the reaction force from the second piezoelectric device, so that the output power of the actuator is reduced. To the contrary, in case of fixing the base member and the chip member on each piezoelectric device by a material having a low rigidity, when the piezoelectric devices are driven by driving voltages having a high frequency, the vibration is absorbed by the adhesive layer, so that the output power of the actuator is reduced.
In the second prior art, a resonance frequency of the piezoelectric device is reduced due to a weight of the resultant motion mechanism, so that the output power of the actuator is reduced. Furthermore, a plurality of resonance vibration modes occur due to the addition of the mechanical members, so that the control of the actuator becomes difficult.